Solid state light emitting devices (LEDs) are being used in an ever increasing variety of applications, and with increased market volume, the cost per device becomes increasingly more important. In like manner, with increased market competition, the relative performance of competing products also becomes increasingly important.
To improve light output efficiency, light emitting devices often include reflective elements that serve to reflect stray light in the intended direction. FIGS. 1A and 1B illustrate example light emitting devices with reflective elements.
In FIG. 1A, the light emitting element 110 is placed in a reflective cup 120, which often also serves as a contact 130 for coupling the element to an external power source. The element 110 will typically include a sandwich configuration of light emitting material between two electrodes, a lower electrode being connected to the contact 130 via the reflective cup 120, and an upper electrode being wire bonded to the other contact 130. The light emitting element 110, the reflective cup 120, and the electrodes 130 are subsequently encapsulated in an encapsulation material 170, such as an epoxy that is molded in the shape of a lens.
In FIG. 1B, the light emitting element 110 is mounted on a substrate 160, and the area surrounding the element 110 is coated with a reflective layer 125, such as a white dielectric. In this example, circuit traces 140 are coupled to the element 110, and through-hole vias 145 couple the traces 140 to electrodes 135 at the lower surface of the substrate 160. In this manner, the light emitting device can be mounted directly upon a printed circuit board or other mounting surface.
The example device of FIG. 1A advantageously includes a reflective cup that is shaped to direct the light output in a concentrated beam, but the manufacturing process requires support of the cup 120 while the light emitting element 110 is mounted and wire bonded, and subsequently encapsulated. The manufacture of example device of FIG. 1B, on the other hand, may be simpler than the manufacture of the device of FIG. 1A, but the encapsulant 150 generally needs to be substantially large and curved for high extraction efficiency and the reflective surface 125 does not direct the light as well as the reflective cup 120.